Nonuniform crossed field electron gun for producing a stable electron beam orbit

ABSTRACT

A NONUNIFORM CROSSED FIELD ELECTRON GUN HAS A LONG THIN ANODE PARALLEL TO THE AXIS OF THE TUBE AND A CATHODE SPACED FROM THE ANODE BY A CONSTANT INTERVAL AND OPPOSITE THE ANODE. AN ELECTRODE OF DIHEDRAL CONFIGURATION HAS A VERTEX WITH AN ELONGATED APERTURE FORMED THEREIN IN THE CENTER AREA OF THE VERTEX. THE CATHODE IS POSITIONED IN THE APERTURE AND THE ELECTRODE OPENS TOWARD THE ANODE. AN ELECTRIC FIELD E(Y) IS PRODUCED IN THE AREA BETWEEN THE ANODE AND THE ELECTRODE TO PROVIDE MOVEMENT OF ELECTRONS IN AXIAL DIRECTION OF THE TUBE. A MAGNETIC FIELD B(Y) IS PRODUCED WHICH HAS A STRENGTH WHICH VARIES AS A FUNCTION OF THE DISTANCE Y FROM THE CATHODE TO THE ANODE IN A DIRECTION TRANSVERSE TO THAT OF THE ELECTRIC   FIELD AND THE AXIS OF THE TUBE. WHEN THE ELECTRIC FIELD AND THE MAGNETIC FIELD ARE IN A POSITION Y=L,   WHEREIN L IS THE POSITION OF THE STABLE ORBIT OF ELECTRONS BETWEEN THE CATHODE AND ANODE, D IS THE CHARGE OF ELECTRONS, M IS THE MASS OF ELECTRONS AND P IS A CONSTANT.

United States Patent [72] Inventors Norihiko Nakayama Kobe-shi;

Minoru Tanaka, Takasago-shi; Eizo Miyauchi, Kawanlshi-shi, Japan [21]Appl. No. 866,202

[22] Filed Oct. 14, 1969 [45] Patented June 28, 1971 [73] AssigneeFujitsu Limited Kawasaki, Japan [32] Priority Oct. 15, 1968 (54]NONUNIFORM CROSSED FIELD ELECTRON GUN FOR PRODUCING A STABLEELECTRONBEAM [56] References Cited UNITED STATES PATENTS 2,680,823 6/1954 Dohleret a1.

2,915,666 12/1959 Bartram 313/156 3,259,789 7/1966 Kluver 3l5/39.3X3,492,531 1/1970 Owakietal 315/326 ABSTRACT: A nonuniform crossed fieldelectron gun has a I long thin anode parallel to the axis of the tubeand a cathode spaced from the anode by a constant interval and oppositethe anode. An electrode of dihedral configuration has a vertex with anelongated aperture formed therein in the center area of the vertex. Thecathode is positioned in the aperture and the electrode opens toward theanode. An electric field B(y) is produced in the area between the anodeand the electrode to provide movement of electrons in axial direction ofthe tube. A magnetic field B( y) is produced which has a strength whichvaries as a function of the distance y from the cathode to the anode ina direction transverse to that of the electric field and the axis of thetube. When the electric field and the magnetic field are in a positiony=L;

P wherein L is the position of the stable orbit of electrons between thecathode and anode, d is the charge of electrons, m is the mass ofelectrons and P is a constant.

PATENTEUJUH28 I971 SHEET 2 OF 2 FIG.4

jELECTRON BEAM FIG.6

NONUNIFORM CROSSED FIELD ELECTRON GUN FOR PRODUCING A STABLE ELECTRONBEAM ORBIT DESCRIPTION OF THE INVENTION Our invention relates to anelectron gun More particularly, the invention relates to a nonuniformcrossed field electron gun.

The electron gun of our invention is particularly adapted for use inelectron tubes such as cathode-ray tubes and travellingwave tubes.

In an electron tube utilizing an electron beam such as, for example, acathode-ray tube, a travelling-wave tube or a velocity modulation tube,the obtaining of a large beam current presents a considerable problem.An increase of the beam current in a cathode-ray tube permits thereduction of high voltage for acceleration and contributes to increasedbrightness. Increased beam current in a travelling-wave tube or avelocity modulation tube contributes to the output power.

Electron guns utilized to produce electron beams in conventionalelectron tubes, as aforedescribed, generally comprise a cathode havingan electron radiating surface directed at right angles to the axis ofthe tube and a plurality of electrostatic electron lenses positionedcoaxially with the cathode. In an electron gun of this type, however,the area of the cathode is limited by the radius of the tube.Furthermore, even if a cathode of large area is utilized, it becomesvery difficult to focus the emitted electrons, and it is thereforeimpossible to provide a beam of a current large enough for presentpurposes. I

In another electron gun developed for use in microwave tubes of aspecific type an electron beam is produced in the direction of the axisof the tube from a plate-shaped cathode having an electron radiatingsurface extending in the direction of the axis of the tube due to theutilization of acrossed field. An electron gun of this type is describedin an article by G. S. Kino, entitled A Design Method For Crossed FieldGuns, IRE Transactions, Volume 7, July, 1960, pages 179 to 185. Theelectron gun described in the Kino article is commonly referred to asthe Kino gun. The Kino gun may provide a slightly larger beam currentthan the electron gun of the firstmentioned type. On' the other hand,however, the Kino gun has a considerably complicated mechanism anddesign. It is therefore extremely difficult to produce a stable electronbeam with the Kino gun. Furthermore, it is practically impossible tofocus the electron beam thinly in the Kino gun.

We have invented an electron gun which is described in pending U.S. Pat.application, Ser. No. 703,513, filed Jan. 22, 1968, now U.S. Pat. No.3,492,531. This electron gun is a special crossed field electron gun andis based on the concept that when an electric field and a magnetic fieldwhich cross each other act on a space in which there is a movement ofelectrons, and the distribution of the magnetic field is made nonuniformso that the distribution is the same as the 2 for l betatron, a stableorbit of electrons is produced in such space. This electron gun isdifferent in principle from the Kino gun and the first-mentioned type ofelectron gun, since it utilizes a magnetic field of nonuniformdistribution. Our previously invented electron gun has the advantagethat there is no limit in theory to the area of the cathode and theradiated electrons may be produced in a stable orbit. This electron gunis described in further detail with reference to FIG. 1.

The electron gun previously invented by us has the disadvantage that itis difficult to focus the electron beam in the lateral direction. Thecross section of the electron beam thus becomes bandshaped or oval,since said electron beam may be focused in the direction of the axis ofthe tube. Although electron beams of such cross-sectional configurationmay be effectively utilized with certain types of objects, they areunsuitable for electron tubes requiring thin beams such as, for example,cathode-ray tubes.

The principal object of the invention is to provide a new and improvednonuniform crossed field electron gun.

An object of the invention is to provide a nonuniform crossed fieldelectron gun which focuses the electron beam in the lateral direction aswell as in the direction of the axis of the tube.

An object of the invention is to provide a nonuniform crossed fieldelectron gun which produces electron beams of large current.

An object of the invention is to provide a nonuniform crossed fieldelectron gun which produces a thinly focused electron beam.

An object of the invention is to provide a nonuniform crossed fieldelectron gun which functions with efficiency, effectiveness andreliability.

In accordance with the invention, a nonuniform crossed field electrongun for a tube having an axis comprises a long thin anode parallel tothe axis of the tube. A cathode is spaced from the anode by a constantinterval and opposite the anode.

An electrode of dihedral configuration has a vertex with an elongatedaperture formed therein in the center area of the vertex. The cathode ispositioned in the aperture formed in the vertex of the electrode. Theelectrode opens toward the anode. Voltage means connected to the anodeand the electrode provides different potentials to the anode and thee1ectrode to produce an electric field E( y) in the area between theanode and the electrode thereby providing movement of electrons in axialdirection of the tube. Magnetic means in operative proximity with thetube produces a magnetic field B(y) having a strength which varies as afunction of the distance y from the cathode to the anode in a directiontransverse to that of the electric field and the axis of the tube. Whenthe electric field E( y) and the magnetic field B( y) are in a positiony=L wherein L is the position of the stable orbit of electrons betweenthe cathode and anode, e is the charge of electrons, m is the mass ofelectrons and P is a constant.

The electrode comprises nonmagnetic material and the magnetic meanscomprises a pair of spaced magnets in operative proximity with the tubein symmetrical positions relative to a plane through the axis of thetube and the longitudinal center of the cathode and in asymmetricalpositions relative to any other plane through the axis of the tube. Themagnet is positioned in a manner whereby like poles of the magnet areopposite each other.

The electrode comprises a pair of thin plates joined to each other indihedral configuration at an angle of substantially The cathode is adirect heated-type cathode extending substantially parallel to the axisof the tube and substantially elongated and thin along its length Thecathode comprises a nickel ribbon. The cathode and the vertex of theelectrode are substantially parallel to the axis of the tube. Thecathode and the vertex of the electrode are oblique to the axis of thetube.

The anode is an elongated thin plate extending parallel to the axis ofthe tube and having a substantially cylindrical trough formed thereinalong its length and opening in the same direction as the electrode. Thecenterline of the trough is the centerline of the anode arid is in avertical plane through the vertex of the electrode.

In order that the invention may be readily carried into effect it willnow be described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of the electron gun disclosed in ourpending U.S. Pat. application, Ser. No. 703,513, now Pat. No. 3,492,531;

FIG. 2 is a schematic diagram illustrating electron focusing based onthe principle of quadruple electrodes;

FIG. 3 is a graphical presentation illustrating the potentialdistribution and the magnetic field distribution in the nonuni-formcrossed field electron gun of the invention;

FIG. 4 is a perspective schematic diagram of an embodiment of thenonuniform crossed field electron gun of the inention;

FIG. is a sectional view taken along the lines v-V of FIG. 41-, and

FIG. 6 is a schematic diagram, partly in axial section, of amodification of the embodiment of FIGS. 4 and 5.

In FIG. I, a plate-shaped anode I is spaced from an electrode 2 and ispositioned in opposition with said electrode. A cathode 3 is provided innearly the same-plane as the electrode 2. The space between the anode 1and the electrode 2 is such that the electrode structure may be regardedas equivalent to part of an annular space for movement of electrons in abetatron, which annular space has an infinitely enlarged radius. The 2for 1 rule of a betatron may be ordinarily expressed as Therefore, ifthe coordinate system of the space provided between the electrodes isdetermined as shown in FIG. 1, and a nonuniformly distributed magneticfield B(y) is applied to the coordinate system in a plane perpendicularto the sheet of illustration, so that the strength of the magnetic fieldsatisfies Equation (l.) as the function of the distance y from the,

cathode 3 to the anode l, a straight stable orbit 4 for the electrons isproduced at the position y=L, as in the case of a betatron. By selectingthe strength of the electric field E, which is provided in a directioncrossing the magnetic field, to a value which will provide the criticalvoltage to electrons moving to the position y=L, electrons 5 radiatedfrom all parts of the cathode 3 are all once collected in the stableorbit 4 in accordance with the cycloidal effect and are provided in theaxial direction of the tube as a single electron beam.

A detailed explanation of the operation of the electron gun of FIG. 1 isprovided in the disclosure of pending patent application, Ser. No.703,513. As hereinbefore stated, it is difficult such voltage to theposition of'the stable orbit determined by the distribution of themagnetic field. The distribution of the electric field for providing thestable orbit may be either uniform or nonuniform. This is evident fromthe following explanation.

In FIG. I, the electrode structure comprises the anode I to which apositive potential is applied, the electrode 2 positioned opposite saidanode and the cathode 3 positioned in essentially the same plane as saidelectrode. Assume that there is a two-dimensional space of movement ofelectrons which comprises the y direction perpendicular to the cathode 3and the x direction parallel to said cathode, a magnetic field lB( y) tofocus the electron beam produced by the electron gun of 1 FIG. l in thelateral direction. When the electrons radiated from the cathode 3 enterinto the straight stable orbit 4, said electrons may be focused in thedirection perpendicular to the surface of said cathode. Such directionis the x direction shown in FIG. 1. As hereinbefore mentioned, focusingcannot be provided in the lateral direction of the cathode, so that thecross-sectional configuration of the electron beam becomes band-shapedor oval.

The electron gun of our invention utilizes the concept of a stable orbitof electrons based on the 2 for 1 rule of the betatron. The electron gunof the invention is superior to the electron guns of other types, sinceit produces electron beams -of large current. The problem of focusingtheelectron beam provided in the stable orbit in a lateral direction issolved in our invention by utilizing the principle of quadrupleelectrodes to provide electron focusing action. In accordance with ourinvention, a ribbon-shaped cathode is spaced from a long thin anodeextending in the axial direction ofthe tube by a constant distance andis opposed to said anode. Instead of plate-shaped electrodes, anelectrode is provided which is of dihedral configuration, or open V typeconfiguration, opening toward the anode and accommodating the cathodealong part ofits vertex. An electric field of nonuniform distributionand a magnetic field of nonuniform distribution are provided incrossingrelation with each other and are applied tothe space of movement ofelectrons between the anode and the dihedral electrode. The electronsfrom the cathode pass through a single stable orbit determined by thecrossed electric and magnetic fields and are derived in the direction ofthe axis of the tube as a thinly focused electron beam. The electron gunof our invention is thus very effectively utilizable in cathode-raytubes.

In the electron gun of FIG. 1, in order to provide a straight or linearstable orbit, it is necessary to provide to the space of movement ofelectrons a magnetic field of nonuniform distribution which satisfiesthe 2 for l rule of the betatron expressed by Equation (I). It is alsonecessary to provide an electric field which will produce a voltage of amagnitude or value suhsmnfiallv Pmml tn the critical vnltaoP and tnannlv perpendicular to the plane of the sheet of illustration andnonuniformly distributed in the y direction, and an electric field B(y)applied to the space of movement of electrons and perpendicularlycrossing the magnetic field and nonuniforrnly distributed in the ydirection. The motion of the electrons radiated from the cathode 3 areordinarily expressed as wherein e is the charge of the electrons, m isthe mass of the electrons and t is the time.

On the other hand, the potential distribution V( Y) and the magneticfield distribution B(y) in the space of movement of electrons maygenerally be expressed as wherein E0 and P are constants which determinethe electric field, b and c are constants which determine the magneticfield distribution, and d is the distance between the cathode 3 and theanode l.

The relation between the potential distribution and the magnetic fielddistribution, expressed by Equations (4) and (6), is illustrated in FIG.3. In FIG. 3, the abscissa represents the distance y from the cathode 3toward the anode l and the ordinate represents the potential V and themagnetic field strength B. The potential distribution curve is indicatedas V( y) and the magnetic field distribution curve is indicated as B(y).In FIG. 3, O is the position of the cathode 3, d is the position of theanode l, b is the strength of the magnetic field at the position of thecathode, 0 is the strength of the magnetic field at the position of theanode and Vd is the anode potential.

In order that a stable orbit may exist inthe space of movemerit ofelectrons, the condition for zero acceleration at the L 2LiB L i=Pf Bon(7) Equation (7) is substantially equivalent to Equation (1) whichrepresents the 2 for 1 rule of the betatron, and a stable orbit isprovided at the position y=L when the magnetic field distribution B( y)satisfies the relation provided by said equation. When an electric fieldsatisfying Equation (8) is applied at thsnneitinn v=l. Electron: 5 frnmthe rmhnrla 3 all enter into the stable orbit It is thus a fact that astable orbit may be provided even if the electric field distributionnonuniform.

In accordance with the invention. an electric field of nonuniformdistribution IS utilized as the electric field in order to provide astable orbit, and a special electrode structure, based on the principleof quadruple electrodes, is utilized in order to focus electrons in thelateral direction under the control of the electric field. The quadrupleelectrode construction is shown in FIG. 2. In FIG. 2, two positivepotential poles 6 and 7 are provided in coplanar position and twonegative potential poles 8 and 9 are provided in coplanar position, theplane of one pair of poles intersecting the plane of the other pair ofpoles at right angles. The positive potential poles 6 and 7 arepositioned opposite each other and the negative potential poles 8 and 9are positioned opposite each other.

In the electrode arrangement shown in FIG. 2, the potential distributionis indicated by the lines 10. The potential indication by lines 11 and12 pass from intermediate positions between positive potential poles andnegative potential poles through the axis between all the poles andbecome zero at such axis. Thus, if an electron beam 13 is provided alongthe axis in a direction perpendicular to the plane of illustration, saidelectron beam is focused so that it has a cross-sectional configuration,illustrated by the crosshatched lines 14, of an oblong elongated in onedirection and compressed in the perpendicular direction.

In accordance with the invention, one quarter of the electrode structureof FIG. 2 including a positive potential pole, is added to the structureof our previous electron gun structure described in pending Pat.application, Ser. No. 703,513. FIGS. 4 and 5 illustrate a preferredembodiment of the electron gun of our invention. In FIGS. 4 and 5, ananode 15 is the equivalent of a positive potential pole of the quadrupleelectrode structure of FIG. 2. An electrode 16,17 is positioned incorrespondence with the zero potential lines 11 and 12 of the quadrupleelectrode structure of FIG. 2 and is provided as a dihedralconfiguration having a vertex with an elongated aperture formed thereinin the center area of the vertex. The electrode 16,17 opens toward theanode 15. A cathode 18 is positioned in the aperture formed in thevertex of the electrode 16,17.

The angle of the dihedral electrode 16,17 is substantially 90. It isnot, however, necessary to strictly regulate this angle. In theillustrated embodiment, the space of movement of electrons is enclosedby the anode 15 and the electrode 16,17. Therefore, in order to providea nonuniform magnetic field in the space of movement of electrons, it isnecessary that the electrode 16,17 comprise nonmagnetic material suchas, for example, copper or stainless steel. The cathode 18 is of directheated-type and comprises a long thin nickel ribbon and an electronradiating material coated on the surface of said ribbon. The cathode 18extends in a direction parallel to the axis of a tube 22, shown inbroken lines, which supports the electron gun structure. The anode 15 isan elongated thin plate extending parallel to the axis of the tube 22and having a substantially semicylindrical trough formed therein alongits length and opening in the same direction as the electrode 16,17. Thecenterline of the trough is the centerline of the anode 15 and is in avertical plane through the vertex of the electrode 16,17.

A suitable supporting arrangement, not shown in the FIGS.

supports the tube housing 22. A suitable voltage source, not shown inthe FIGS. is connected from outside the tube 22 to the electrodes 16,17in the electron gun structure, as well as to the anode 15 and thecathode 18. It is especially desirable to support one end of the cathode18 with spring bias, so thatthermal expansion may be compensated for.

If it is assumed that a positive potential is applied to the anode 15and a zero, or slightly negative potential is applied to the electrode16,17 in the structure of FIGS. 4 and 5, an electric field of nonuniformdistribution similar to that in the region of one-quarter of thequadruple electrode structure trons enclosed by said anode and saidelectrode, in accordance with Equation (4). This potential distributionis shown in FIGS. 5 and 6 by the equipotential broken lines 19. Theelectrons 5 radiated from the cathode 18 are directed toward the anode15 and are focused in the lateral direction within the nonuniformelectric field, in accordance with the principle of quadrupleelectrodes. If a magnetic field of nonuniform distribution, satisfyingEquation (7), is provided, however, in a direction crossing the electricfield, the electrons 5 are collected in a stable orbit and are thinlyfocused in the lateral direction as well. The nonuniform magnetic fieldmay be provided, for example, by a pair of magnets 20 and 21, as shownin FIG. 5. The magnets 20 and 21 are spaced'from each other and are inoperative proximity with the tube 22 in symmetrical positions relativeto a plane through the axis of said tube and the longitudinal center ofthe cathode 18. The magnets 20 and 21 are in asymmetrical positionsrelative to any other plane through the axis of the tube 22..

Each of the magnets 20 and 21 has a curved pole face which correspondswith the wall of the tube 22. The magnets 20 and Y 21 are asymmetricalrelative to the axis of the tube 22 in a manner whereby like poles ofsaid magnets are opposite each other. Magnetic lines of force 23 inFIGS. 4 and 5 illustrate the condition of the magnetic field provided bythe magnets 20 and 21 in the space of movement of electrons. In FIGS. 4and 5, the magnetic field is provided in a distribution which is strongon the side of the cathode 18 and is gradually weakened as it approachesthe anode 15. Needless to say, however, the magnetic field may also beprovided in a distribution which increases as the anode 15 isapproached, as far as Equations (7) and (8) are satisfied.

Equation (8) may be rewritten as Equation (9), in order to express theanode voltage Vd.

2.5.1. 2-P p =,T[ (L i (9) The relation between L and the constants maybe expressed by substituting Equation (6) for Equation (7).

as bc [P-4 (10) Since the position L of the stable orbit is within therange O L Ad, the range ofP is determined as follows:

When b c, which indicates a decreasing magnetic field,

When b c, which indicates an increasing magnetic field,

Therefore, if L equals d/2, so that the position of the stable orbit isjust at the intermediate position between the cathode 18 and the anode15, the following equation is derived from Equation (10).

Ifd and L are selected as d=5 times l0 m and L=2.5 times 10 m, and if band c are selected as b=l00 times 1O wb/m and c =0 wb/m, so that themagnetic field strength at the position of the stable orbit L becomes 50times 10 wb/m Equation 13) may be expressed as P=4/3 and c/b=0.Therefore, if a voltage of 78 volts, derived from Equation (9), isapplied to the anode 15, and a magnetic field B(y) =200 times 10 y 10wb/m. derived from Equation (6), is applied between the anode and thecathode, Equations (7) and (8) are satisfied at the intermediateposition between the anode and the cathode; that is, the position L=2.5times 10 m. A stable orbit is thus formed at this position.

Similarly. if h=l6.66 times l wb/m and if (=83 33 times l0 wb/m. c/bbecomes 5. If such an increasing magnetic field, which increases fromthe cathode 18 as the reference toward the anode 15. is applied. P maybe expressed as P=3 from Equation l 3 The anode voltage is then 48.85volts and the magnetic field is B(y)=l33.4 times y+0.l666 times l0 wblmA stable orbit may thus be provided at the position L=2.5 times 10 m. i

FIG. 6 illustrates a modification of the embodiment of FIGS. 4 and 5. Inthe modification of FIG. 6, the cathode l8 and the vertex of theelectrode 16', 17' extend obliquely with .or inclined to the axis of thetube 22. In the embodiment of FIGS. 4 and 5, the cathode ll8 and thevertex of the electrode 16,17 extend parallel to the axis of the tube22. It has been confirmed by experiment that by positioning the cathodeobliquely to the axis of the tube 22, the force of the electric field,as against the electrons, may be provided with a component in the axialor x direction. This results in a reduction of the suppression effect onelectrons by the space charge. It is desirable to select the angle ofinclination of the cathode 18' relative to the axis of the tube 22 asfrom 5 to 6.

FIG. 6 illustrates a first grid 24 for acceleration of electrons, amagnet 25 for prefocusing of electrons and a second grid 26. The firstgrid 24 for the acceleration of the electrons has the same potentialapplied to it as that applied to the anode 15. The first grid 24, themagnet 25 and the second grid 26 function as the principal electronlens.

While the invention has been described by means of specific examples andin specific embodiments, we do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

We claim:

1. A nonuniform crossed field electron gun for a tube having an axis,said electron gun comprising a long thin anode parallel to the axis ofthe tube;

a cathode spaced from said anode by a constant interval and oppositesaid, anode;

an electrode of dihedral configuration having a vertex with an elongatedaperture formed therein in the center area of said vertex, said cathodebeing positioned in the aperture formed in the vertex of said electrode,said electrode opening toward said anode;

voltage means connected to said anode and said electrode for providingdifferent potentials to said anode and said electrode to produce anelectric field B(y) in the area between said anode and said electrodethereby providing movement of electrons in axial direction of said tube;

magnetic means in operative proximity with said tube for producing amagnetic field B(y) having a strength which varies as a function of thedistancey from said cathode to said anode in a direction transverse tothat of the electric field and the axis of the tube, wherein when saidelectric field E( y) and said magnetic field B(y) are in a position y=L.

l: (L) P wherein L is the position of the stable orbit of electronsbetween the cathode and anode, e is the charge of electrons, m is themass of electrons and P is a constant.

2. A nonuniform crossed field electron gun as claimed in claim 1,wherein said electrode comprises nonmagnetic material and said magneticmeans comprises a pair of spaced magnets in operative proximity with thetube in symmetrical positions relative to a plane through the axis ofthe tube and the longitudinal center of the cathode and in asymmetricalpositionsrelative to any other plane through the axis of the tube, saidmagnets being positioned in a manner whereby like poles of said magnetsare opposite each other.

3. A nonuniform crossed field electron gun as claimed in claim 1,wherein said electrode comprises a pair of thin plates joined to eachother in dihedral configuration at an angle of substantially 90.

4. A nonuniform crossed field electron gun as claimed in claim 1,wherein said cathode is a direct heated-type cathode extendingsubstantially parallel to the axis of the tube and sub stantiallyelongated and thin along its length, said cathode '7. A nonuniformcrossed field electron gun as claimed in claim 3, wherein said anode isan elongated thin plate extending parallel to the axis of the tube andhaving a substantially semicylindrical trough formed therein along itslength and opening in the same direction as said electrode, thecenterline of the trough being the centerline of the anode and being ina vertical plane through the vertex of said electrode.

